With the improvement of people's living standards, people's demand for the stability of a liquid crystal display is becoming higher and higher. Thus, it is required that patterns of various functional layers (e.g., an active layer, a source, a drain, a data line, a gate line, a pixel electrode, respective insulating layers, etc.) of a display panel have a good uniformity of size.
It is known that, in the formation of various functional layers of a display panel, the functional layers are generally subject to a lithography process usually including four procedures: photoresist coating, exposure, development, and etching, wherein the process capability and stability of each procedure have a direct influence on the sizes of patterns of various finally-formed functional layers. For example, nonuniformity in photoresist coating will directly result in nonuniformity of the sizes of patterns of various functional layers formed after exposure, then, the procedure of exposure will directly result in nonuniformity of the sizes of patterns of various functional layers after development, further, the procedure of development directly results in nonuniformity of the sizes of patterns of various functional layers after etching, all of which will severely affect the performance of the display panel.
In an actual lithography process, the inventors found that in the procedure of photoresist coating, a thickness of the photoresist-film layer normally coated on a glass substrate generally tends to be thin in the central region and thick in the periphery, and there is a case where the thicknesses of different positions in different regions are irregular. Furthermore, the inventors also found that even for different glass substrates in the same batch, the coating thicknesses of the photoresist-film layers are not entirely the same. It can be said that the thicknesses of photoresist-film layers in different glass substrates and in different positions of a single glass substrate are different in a procedure of photoresist coating.
The structure of a conventional exposure apparatus is shown in FIG. 1 (a mirror projection exposure apparatus is taken as an example here). A photoresist-film layer 8 is directly exposed to light emitted from a light source 1 and having passed through a mask plate 6 and a lens group 7. Since exposure-light intensities in different positions or regions of the photoresist-film layer 8 are the same, with this exposure apparatus, patterns of various functional layers formed after exposure will be non-uniform in size, which easily results in defects in various functional layers, and even affects the stability of a liquid crystal panel.